"So how come you play a right handed guitar upside-down and left handed?" is a question I am often asked. It wasn't a stylistic of fashion choice...
When I started out I joined a band with some twins. They were a drummer and a guitarist and had a bass also. I had nothing and sang and played their bass. It was a right handed one and being left handed I just turned it upside down. When another friend joines he became the bass player as that was the easiest instrument to learn and I moved to guitar and vocal graduating to a a right handed electric guitar.
After that it was too late. I had committed too far to switch so just carried on upside down. In my early punk bands this was an issue as I would often break the top E string, that being the thinnest and the one I hit first. The style also still defines my sound to this day. Hitting the top strings first gives me a more treble sound allowing the vocal to come to the fore.
Like anything it has its drawbacks. There are simple chords i can't play because it's upside down but equally there are others that would not be available in a conventional style>
So left handed it is and that's the story why.